Thermoplastic elastomer composition for powder slush molding and process for preparation of said composition

ABSTRACT

A thermoplastic elastomer composition for powder slush molding made up of a polypropylene resin, hydrogenated styrene/butadiene rubber, a process oil and an elastomer excellent in oil absorbing power. A process for making that thermoplastic elastomer composition may include the addition of an organic peroxide to the above components and kneading the obtained mixture while heating.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a thermoplastic elastomer composition forpowder slush molding and a process for the preparation of thatcomposition. More specifically, the invention relates to a thermoplasticelastomer composition having a high degree of fluidity in a powderystate and a low melt viscosity, and which may enable the easy release ofa molded skin from a mold.

2. Background Art

Powder slush molding processes are widely employed in the automotiveindustry to form the skins of instrument panels, console boxes, doortrims, and other interior trims in automobiles. The skins are soft tothe touch, allow for leather graining and stitching, and permit greatdesign freedom. Unlike injection or compression molding, no pressure isapplied for shaping in powder molding processes. Therefore, the powderymaterial for powder slush molding ideally should not only have a highdegree of fluidity in the powdery state so as to attain the uniformadhesion of the material to a mold having a complicated shape, butshould also exhibit a low melt viscosity so that it can be molten andfluidized without pressing to form a film. Furthermore, it is desirablethat the skin layer formed on a mold release easily from the mold aftercooling.

A powder material composition designed to meet these goals has beenproposed in Japanese Pat. Appln. Laid-Open Gazette No. Hei 7-82433.Disclosed therein is a powder slush molding material prepared bypulverizing a mixture made up of a polypropylene resin and a specifiedstyrenic thermoplastic elastomer at a weight ratio between 70:30 and30:70. The styrenic thermoplastic elastomer is chosen from amongstyrene/ethylene/butylene/styrene block copolymers,styrene/ethylene/propylene/styrene block copolymers, and hydrogenatedstyrene/butadiene rubbers, with all having a styrene content of no morethan 20% by weight. Compositions with each of these elastomers aresuitable for powder molding.

However, the composition made up of the polypropylene resin and ahydrogenated styrene/butadiene rubber is particularly problematic inthat the oligomeric component contained in the composition bleeds to thesurface because of the poor oil absorbing power of the hydrogenatedstyrene/butadiene rubber. This makes the composition sticky, causingaggregation and poor fluidity in the powdery state. This also makes itdifficult to release skins from molds.

SUMMARY OF THE INVENTION

The present invention has as one of its objectives to solve the aboveproblems by providing a thermoplastic elastomer composition for powderslush molding which makes possible excellent melt flow propertiessuitable for powder molding, a low melt viscosity, and the facilitatedrelease of a molded skin from a mold. The present invention is alsodirected to a process for the preparation of such a composition.

In one form of the invention, a thermoplastic elastomer composition isprovided for powder slush molding which made up of a polypropyleneresin, a hydrogenated styrene/butadiene rubber, a process oil, and anelastomer excellent in oil absorbing power.

In one form, the thermoplastic elastomer composition has a melt flowrate of at least 5 g/10 min as determined according to JIS K-7210 at250° C. under a load of 0.325 kgf

In one form, the weight ratio in the composition of the polypropyleneresin to the hydrogenated styrene/butadiene rubber is between 80:20 and20:80.

The elastomer excellent in oil absorbing power may be mixed in thecomposition in an amount of 20 to 250 parts by weight per 100 parts byweight of the hydrogenated styrene/butadiene rubber.

In one form, the elastomer excellent in oil absorbing power is selectedfrom among styrene/ethylene/propylene/styrene block copolymers,styrene/ethylene/butylene/styrene block copolymers, crystallineolefin/ethylene/butylene/crystalline olefin block copolymers,ethylene/propylene rubbers, and ethylene/octene copolymers.

In one form, the process oil is mixed in the composition in an amount of5 to 200 parts by weight per 100 parts by weight of the elastomerexcellent in oil absorbing power.

In one form of the invention, a thermoplastic elastomer composition isprovided for powder slush molding which is made up of a polypropyleneresin, a hydrogenated styrene/butadiene rubber, a process oil, anelastomer excellent in oil absorbing power, and an organic peroxide.

The thermoplastic elastomer composition may be made up of apolypropylene resin, a hydrogenated styrene/butadiene rubber, a processoil, and an elastomer excellent in oil absorbing power. The compositionmay be formed by preparing a blend of the polypropylene resin and thehydrogenated styrene/butadiene rubber at a weight ratio between 80:20and 20:80, adding an elastomer excellent in oil absorbing power to theblend in the amount of 20 to 250 parts by weight per 100 parts by weightof the hydrogenated styrene/butadiene rubber, adding a process oil tothe blend in the amount of 5 to 200 parts by weight per 100 parts byweight of the elastomer excellent in oil absorbing power, kneading andpelletizing the resulting composition, and pulverizing the obtainedpellets either at ambient temperature or in a frozen state.

In one form, a process for the preparation of a thermoplastic elastomercomposition, according to the invention, includes the steps of adding ahydrogenated styrene/butadiene rubber, a process oil, an elastomerexcellent in oil absorbing power, and an organic peroxide to apolypropylene resin and kneading the obtained mixture.

In one form, the organic peroxide is added during the process in anamount of 0.02 to 5.0% by weight based on the thermoplastic elastomercomposition and the kneading is conducted at a temperature of 120 to250° C.

In another form of the invention, a process for the preparation of athermoplastic elastomer composition includes the steps of adding ahydrogenated styrene/butadiene rubber, a process oil, an elastomerexcellent in oil absorbing power and an organic peroxide to apolypropylene resin at such a mixing ratio that the weight ratio of thepolypropylene resin to the hydrogenated styrene/butadiene rubber liesbetween 80:20 and 20:80, the amount of the elastomer excellent inoil-absorbing power is 20 to 250 parts by weight per 100 parts by weightof the hydrogenated styrene/butadiene rubber, and the amount of theprocess oil is 5 to 200 parts by weight of the elastomer excellent inoil absorbing power; kneading and pelletizing the obtained mixture as itis heated; and pulverizing the obtained pellets either at ambienttemperature or in a frozen state. The kneading may be conducted at atemperature of 120 to 250° C.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In one form of the invention, a thermoplastic elastomer composition ismade up of a polypropylene resin, a hydrogenated styrene/butadienerubber, a process oil, and an elastomer excellent in oil absorbingpower.

The polypropylene resin to be used in the present invention is selectedfrom among homopolymers of polypropylene and block and random copolymersthereof with α-olefins. For the greatest flexibility of the molding, itis preferable to use a block or random copolymer wherein the α-olefin isethylene. Also, the polypropylene resin must exhibit a melt flow rate(MFR) of 20 g/10 min or higher as determined according to JIS K 7210 at230° C. under a load of 2.16 kgf. A property of the above polypropyleneresins is that their backbone may be cleaved by heat or throughoxidation. This is in contrast with polyethylene which becomescross-linked or cured by heat or through oxidation. Thus, the molecularweight of polypropylene resins may be lowered in the thermoplasticelastomer composition through the addition of, for example, an organicperoxide.

A hydrogenated styrene butadiene rubber (H-SBR) is used because of itsexcellent compatibility with the polypropylene resin. A thermoplasticelastomer composition prepared with both is flexible enough that littlewhitening appears when bending the material. The styrene content of thehydrogenated styrene/butadiene rubber to be used is preferably no morethan 30% by weight, and a content of 5 to 15% by weight is preferred toform a flexible skin.

The mixing ratio of the polypropylene resin to H-SBR ranges from 80:20to 20:80 by weight. When the amount of the resin is too large, theresulting molded skin will be too hard. If the resin amount is toosmall, the skin will have poor tensile strength.

The composition also contains a process oil which is absorbed into theelastomer components of the composition. This serves to lower the meltviscosity of the composition and makes it possible to produce a soft,flexible skin. The process oil may be any of those used conventionallyfor rubbers, including paraffin oils, naphthene oils and aromatic oils,with paraffin oils being preferable because of their compatibility withthe elastomer components. The addition amount of the process oil isideally 5 to 200 parts by weight per 100 parts by weight of elastomerexcellent in oil absorbing power. When the proportion exceeds 200 partsby weight, the tensile properties may be poor. When it is less than 5parts by weight, the resulting composition may not have a sufficientlylowered melt viscosity and the skin formed may be overly hard.

The elastomer excellent in oil absorbing power must be compatible withthe polypropylene resin and have the property of absorbing the processoil and the oligomeric component contained in the composition. Examplesof such an elastomer include styrenic block copolymer type thermoplasticelastomers such as styrene/ethylene/butylene/styrene block copolymers(SEBS), styrene/ethylene/propylene/styrene block copolymers (SEPS),crystalline olefin/ethylene/butylene/crystalline olefin block copolymers(CEBC), ethylene/propylene rubbers (EPR), and ethylene/octene copolymers(POE).

SEBS is a product of hydrogenation of a styrene/butadiene/styrene blockcopolymer (SBS), and commercially available examples thereof includeCLAYTON G™ series (products of Shell Chemical) and TUFTEC E™ series(products of Asahi Chemical Industry). SEBS has a property that as thestyrene content increases, the strength is enhanced and the flexibilitydecreases. Furthermore, in slush molding, molten SEBS tends to cause theaggregation of styrene hard segments and fails to form a smooth,sheet-like product. It is therefore preferable that the styrene contentbe no more than 40% by weight in elastomers of this type.

SEPS is a product of the hydrogenation of a styrene/isoprene/styreneblock copolymer (SIS), and a representative commercially availableexample thereof is SEPTON™ (a product of Kuraray). SEPS, like SEBS,lowers in flexibility as its styrene content increases, so that thestyrene content of SEPS is also preferably no more than 40% by weight.

If a thermoplastic elastomer composition with H-SBR does not contain anelastomer excellent in oil absorbing power, it will be sticky becausethe oligomeric component contained in the composition bleeds to thesurface because of the poor oil absorbing power of H-SBR. Therefore, apowdery material for powder slush molding prepared by pulverizing thiscomposition is also sticky and has poor fluidity. It is difficult toremove a skin formed made from this material from a mold. The presentinvention solves this problem by providing an elastomer to absorb theoil.

The amount of the above elastomer excellent in oil absorbing powerpresent in the composition is 20 to 250 parts by weight per 100 parts byweight of the H-SBR. When the amount is less than 20 parts by weight,the oligomeric component and the oil contained in the composition maynot be sufficiently absorbed. If the amount exceeds 250 parts by weight,the dispersion of the elastomer in the propylene resin may be inadequateand result in a skin with poor tensile properties.

An organic peroxide may also be added to the composition. It may be anyone conventionally used in the cross-linking of resins or rubbers.Examples include diacyl peroxides, peroxy esters, diallyl peroxide,di-t-butyl peroxide, t-butyl cumyl peroxide, dicumyl peroxide,2,5-dimethyl-2,5-di(t-butylperoxy)hexane-3,1,3-bis(t-butylperoxyisopropyl)benzene,and 1,1-dibutylperoxy-3,3,5-trimethylcyclohexane. It is preferable thatthe organic peroxide exhibit a one minute half-life temperature of 150to 250° C. in thermal decomposition.

The organic peroxide causes the cleavage of the polypropylene resinbackbone when kneading at a temperature of 120 to 250° C. This lowersthe molecular weight of the resin and thus enhances the melt flowproperties of the thermoplastic elastomer composition. The organicperoxide is added in an amount of 0.02 to 5.0% by weight based on thethermoplastic elastomer composition. When the amount is less than thisrange, excellent melt flow properties may not result because the resinbackbone may not be effectively cleaved. If the amount exceeds thisrange, excessive decomposition may occur and result in a molded articlewhich is poor in mechanical characteristics such as tensile strength.

The inventive composition may also contain conventional heat stabilizersfor polyolefins. A combination of a phenolic antioxidant with aphosphite antioxidant is generally used, though the heat stabilizer tobe used in the present invention is not particularly limited.

Furthermore, the composition may contain a light stabilizer, andexamples thereof include hindered amines and bensotriazoles serving asradical scavengers. The composition may also contain a pigment selectedfrom among ordinary organic and inorganic pigments suitable for olefins.If necessary, the composition may also include a lubricant selected fromamong metal salts of fatty acids, and/or a filler such as calciumcarbonate or talc.

The mixing of the above components is accomplished by dry blending apolypropylene resin, H-SBR, an elastomer excellent in oil absorbingpower, a pigment, a stabilizer and a lubricant together in a twincylinder mixer, tumbler, Henschel mixer, or the like. The obtained blendis then fed into a twin screw extruder through a feed hopper whilepouring in a process oil through a vent hole. An extruder thenmelt-kneads the composition at a temperature of 120 to 250° C. and theextrusion is pelletized.

If an organic peroxide is added, mixing is accomplished in a similarmanner except that a filler is also added. Alternatively, the mixing ofthe components in this case can also be conducted by kneading theelastomer components (i.e., H-SBR and an elastomer excellent in oilabsorbing power) with a process oil using a kneader or Banbury mixer;pelletizing the obtained mixture; adding a polypropylene resin, anorganic peroxide and the other components to the obtained pellets; andconducting melt-kneading and pelletization of the resulting mixture bythe use of a single or twin screw extruder at a temperature of 120 to250° C.

The addition of a heat stabilizer and/or light stabilizer isnecessitated depending on the field of application of the resultingpower-molded article. These stabilizers, however, hinder thedecomposition of the polypropylene resin by the organic peroxide. It istherefore preferable to mix and knead these stabilizers with the othercomponents by the use of an extruder only after the above pelletization.

It is preferable that the pellets exhibit a melt flow rate (MFR) of 5g/10 min or higher as determined according to JIS K7210 at 250° C. undera load of 0.325 kgf. When the MFR is less than this value, the resultingcomposition may be poor in melt flow properties and may result in a skinhaving pinholes therein.

An impact mill such as a turbo mill, pin mill or hammer mill thenpulverizes the pellets. This is generally conducted after the pelletsare frozen with liquid nitrogen. When the pulverization is conducted atambient temperature, only a coarse powder is obtained in some cases dueto stringing.

The powder thus obtained is screened to collect particles passingthrough at least a sieve of 1000 μm and having a mean diameter of 100 to800 μm, and an organic or inorganic powder improver is added to thecollected particles, followed by mixing.

Powder slush molding is then conducted by the use of the powderyelastomer composition prepared above. In this molding, the powderycomposition is thrown mainly by gravity into a mold heated at atemperature equal to or exceeding the melting point of the composition.After the lapse of a predetermined time, the mold is inverted to recoverexcessive powder into a box. A layer of the composition adhering to thesurface of the mold is progressively made molten to form a skin layer.The mold is cooled and the skin layer is removed from the mold.

The mold is heated generally either by oil circulation or by placing itin a hot air oven. When the formed method is employed, the moldtemperature can easily be controlled by regulating the arrangement ofpipes, but the heating is limited only to the mold side. On the otherhand, the use of a hot air oven makes it possible to heat the skin fromboth the mold side and the back side of the skin. However, hot air of300° C. or above is generally used, so the conditions must be selectedso as not to cause the degradation of the back of the skin throughthermal oxidation.

The present invention will now be described in more detail by referenceto the following examples.

INVENTIVE COMPOSITIONS 1-5

The materials listed in Table 1, except the process oil, weredry-blended together in a tumbler. The obtained blends were fed into atwin screw extruder through a feed hopper while the process oil wasinserted through a vent hole. The materials were extruded at 200° C. andpelletized. The obtained pellets were immersed in liquid nitrogen,thrown into a turbo mill and pulverized. The obtained powders werescreened to collect only particles passing through a sieve of 1000 μm.

                                      TABLE 1                                     __________________________________________________________________________              Parts by weight                                                     Component Composition 1                                                                        Composition 2                                                                        Composition 3                                                                        Composition 4                                                                        Composition 5                           __________________________________________________________________________    polypropylene resin.sup.1                                                               56     56     56     56     56                                      H-SBR.sup.2                                                                             19     19     19     19     19                                      SEPS.sup.3                                                                              9      --     --     --     8                                       SEBS.sup.4                                                                              --     9      --     --     --                                      CEBC.sup.5                                                                              --     --     9      --     --                                      EPR.sup.6 --     --     --     9      --                                      process oil.sup.7                                                                       12     12     12     12     15                                      pigment   4      4      4      4      4                                       Ca stearate                                                                             0.5    0.5    0.5    0.5    0.5                                     phenolic antioxidant                                                                    0.1    0.1    0.1    0.1    0.1                                     phosphite antioxidant                                                                   0.1    0.1    0.1    0.1    0.1                                     __________________________________________________________________________     .sup.1 CHISSO POLYPRO K7750 ™ (a product of Chisso Corp.), MFR             (230° C., 2.16 kgf): 45 g/10 min                                       .sup.2 DYNARON 1320P ™ (a product of Japan Synthetic Rubber), styrene      content: 10 wt %, MFR (230° C., 2.16 kgf): 3.5 g/10 min                .sup.3 Styrene/ethylene/propylene/styrene block copolymer (SEPS), SEPTON      2063 ™ (a product of KURARAY), styrene content: 13 wt %, MFR               (230° C., 2.16 kgf): 7 g/10 min                                        .sup.4 Styrene/ethylene/butylene/styrene block copolymer (SEBS), TUFTEC       H1052 ™ (a product of Asahi Chemical Industry), styrene content: 20 wt     %, MFR (230° C., 2.16 kgf): 12 g/10 min                                .sup.5 Crystalline olefin/ethylene/butylene/crystalline olefin (CEBC),        DYNARON 6200P ™ (a product of Japan Synthetic Rubber), MFR(230°     C., 2.16 kgf): 2.5 g/10 min                                                   .sup.6 Ethylene/propylene rubber (EPR), EP914P ™ (a product of Japan       Synthetic Rubber), propylene content: 22 wt %, MFR(230° C., 2.16       kgf): 8.6 g/10 min                                                            .sup.7 DIANA ™ Process Oil (a product of IDEMITSU KOSAN), PW: 380     

Powder slush molding was carried out using the above compositions. Aleather-grained plate (150 mm×150 mm×3 mm) was heated to 250° C. in anoven. 800 g of a composition was spread thereon and made to adhere tothe plate by allowing a time period of 10 minutes. Any material notadhering was removed. The resulting plate was oven-heated at 300° C. for60 seconds, removed from the oven, and cooled with water. Finally, askin with a thickness of 0.8 mm was removed from the plate.

For each example, the melt viscosity of the pellets, the tensileproperties of the skin, releasability from the mold, and powderinesswere all evaluated by the following methods. The melt viscosity wasevaluated by determining the MFR of the pellets according to JIS K7210at 250° C. under a load of 0.325 kgf. The tensile properties wereevaluated by punching a specimen out of each skin using a JIS No.3dumbbell die and determining the tensile strength and elongation of eachspecimen at a pulling rate of 200 mm/min. The releasability from themold was evaluated by heating a bastard cut file having a thickness of 3mm, a width of 17 mm, and a length of 180 mm to 250° C. in an oven, andforming a skin thereon with each composition. The formed skin was peeledat a rate of 500 mm/min to determine the force necessary for peeling.The powderiness was evaluated by adding a powderiness improver to eachcomposition and determining the angle of repose of the resulting mixtureby the use of a powder tester (mfd. by Horikawa Micron).

The results of these tests are given in Table 2, below.

                                      TABLE 2                                     __________________________________________________________________________    Property     Example 1                                                                          Example 2                                                                          Example 3                                                                          Example 4                                                                          Example 5                                    __________________________________________________________________________    MFR(250° C., 0.325 kgf)                                                             7.8  10.5 7.1  6.7  9.6                                          Tensile Strength (N/cm.sup.2)                                                              965  957  972  826  813                                          Elongation(%)                                                                              683  680  691  589  572                                          JIS A Hardness                                                                             86   87   86   86   83                                           Mold Release Test(N)                                                                       4.9  4.6  4.8  4.2  4.6                                          Angle of repose of powder (°)                                                       37   38   38   39   39                                           __________________________________________________________________________

COMPARATIVE COMPOSITIONS 6-8

Compositions 6-8 were prepared and evaluated in the same manner as thatof Composition 1 except that the elastomer excellent in oil absorbingpower and the process oil were not used. The compositions are detailedin Table 3 and the results are given in Table 4, both of which appearbelow.

                  TABLE 3                                                         ______________________________________                                                 Parts by weight                                                      Component  Composition 6                                                                             Composition 7                                                                            Composition 8                               ______________________________________                                        polypropylene resin.sup.8                                                                56          56         56                                          H-SBR.sup.9                                                                              28          48         9                                           SEPS.sup.10                                                                              --          --         19                                          SEBS.sup.11                                                                              --          9          --                                          CEBC.sup.12                                                                              --          --         --                                          EPR.sup.13 --          --         --                                          process oil.sup.14                                                                       12          --         --                                          pigment    4           4          4                                           Ca stearate                                                                              0.5         0.5        0.5                                         phenolic antioxidant                                                                     0.1         0.1        0.1                                         phosphite  0.1         0.1        0.1                                         antioxidant                                                                   ______________________________________                                         .sup.8 CHISSO POLYPRO K7750 ™ (a product of Chisso Corp.), MFR             (230° C., 2.16 kgf): 45 g/10 min                                       .sup.9 DYNARON 1320P ™ (a product of Japan Synthetic Rubber), styrene      content: 10 wt %, MFR (230° C., 2.16 kgf): 3.5 g/10 min                .sup.10 Styrene/ethylene/propylene/styrene block copolymer (SEPS), SEPTON     2063 ™ (a product of KURARAY), styrene content: 13 wt %, MFR               (230° C., 2.16 kgf): 7 g/10 min                                        .sup.11 Styrene/ethylene/butylene/styrene block copolymer (SEBS), TUFTEC      H1052 ™ (a product of Asahi Chemical Industry), styrene content: 20 wt     %, MFR (230° C., 2.16 kgf): 12 g/10 min                                .sup.12 Crystalline olefin/ethylene/butylene/crystalline olefin (CEBC),       DYNARON 6200P ™ (a product of Japan Synthetic Rubber), MFR (230.degree     C., 2.16 kgf): 2.5 g/10 min                                                   .sup.13 Ethylene/propylene rubber (EPR), EP914P ™ (a product of Japan      Synthetic Rubber), propylene content: 22 wt %, MFR (230° C., 2.16      kgf): 8.6 g/10 min                                                            .sup.14 DIANA ™ Process Oil (a product of IDEMITSU KOSAN), PW: 380    

                  TABLE 4                                                         ______________________________________                                                        Composi- Composi-  Composi-                                   Property        tion 6   tion 7    tion 8                                     ______________________________________                                        MFR (250° C., 0.325 kgf)                                                               7.0      2.8       3.7                                        Tensile Strength (N/cm.sup.2)                                                                 982      1035      626                                        Elongation (%)  653      717       513                                        JIS A Hardness  84       89        90                                         Mold Release Test (N)                                                                         6.8      13.4      10.3                                       Angle of repose of powder (°)                                                          42       40        35                                         ______________________________________                                    

In comparative Composition 6, the powdery composition had a large angleof repose and was quite sticky, resulting in a skin with many pinholes.In comparative Composition 7, the skin was hard and also had pinholesdue to the poor melt flow properties. Furthermore, in comparativeComposition 8, the dispersed SEPS particles were too large to form askin with satisfactory tensile properties.

On the contrary, inventive Compositions 1-5 showed no pinholing due toenhanced melt flow and lowered stickiness as compared with comparativeCompositions 6-8. Also, the peel forces observed in inventiveCompositions 1-5 were smaller than those of comparative Compositions6-8.

INVENTIVE COMPOSITIONS 9-12

In a manner similar to that used for Compositions 1-5, the materialslisted in Table 5, below, except the process oil, were dry-blendedtogether in a tumbler. Obtained blends were fed into a twin screwextruder through a feed hopper while the process oil was insertedthrough a vent hole. The materials were extruded at 200° C. andpelletized. Then, the obtained pellets were immersed in liquid nitrogen,thrown into a turbo mill, and pulverized. Obtained powders were screenedto collect only particles passing through a sieve of 1000 μm.

                                      TABLE 5                                     __________________________________________________________________________              parts by weight                                                     Component Composition 9                                                                        Composition 10                                                                        Composition 11                                                                        Composition 12                               __________________________________________________________________________    polypropylene resin.sup.15                                                              56     51      56      51                                           H-SBR.sup.16                                                                            13     14      13      14                                           POE.sup.17                                                                              15     23      --      --                                           EPR.sup.18                                                                              --     --      15      23                                           process oil.sup.19                                                                      12     8       12      8                                            pigment   4      4       4       4                                            Ca stearate                                                                             0.5    0.5     0.5     0.5                                          phenolic antioxidant                                                                    0.1    0.1     0.1     0.1                                          phosphite antioxidant                                                                   0.1    0.1     0.1     0.1                                          __________________________________________________________________________     .sup.15 CHISSO POLYPRO XK0286 ™ (a product of Chisso Corp.), MFR           (230° C., 2.16 kgf): 27 g/10 min                                       .sup.16 DYNARON 1320P ™ ™ (a product of Japan Synthetic Rubber),        styrene content: 10 wt %, MFR (230° C., 2.16 kgf): 3.5 g/10 min        .sup.17 ENGAGE EG8400  ™ (a product of DuPont Dow Elastomers L.L.C.),      MFR (230° C., 2.16 kgf): 30 g/10 min, octene content: 24 wt %.         .sup.18 Ethylene/propylene rubber (EPR), EP914 ™ (a product of Japan       Synthetic Rubber), propylene content: 22 wt %, MFR (230° C., 2.16      kgf): 8.6 g/10 min                                                            .sup.19 DIANA ™ Process Oil (a product of IDEMITSU KOSAN), PW: 380    

In a manner similar to that used for inventive Compositions 1-5, powderslush molding was conducted using Compositions 9-12 to form skins havinga thickness of about 0.8 mm. Evaluation of the pellet melt viscosity,skin tensile properties, skin releasability from the mold, andpowderiness were performed. The results are given in Table 6, below.

                                      TABLE 6                                     __________________________________________________________________________                Composition                                                       Property    9     Composition 10                                                                        Composition 11                                                                        Composition 12                              __________________________________________________________________________    MFR (250° C., 0.325 kgf)                                                           8.1   5.8     7.3     5.1                                         Tensile Strength (N/cm.sup.2)                                                             1124  985     1012    871                                         JIS A Hardness                                                                            87    86      86      85                                          Mold Release Test (N)                                                                     4.2   4.9     4.3     5.0                                         Angle of repose of                                                                        38    37      38      39                                          powder (°)                                                             __________________________________________________________________________

It can be understood from these results that the powdery compositionsexhibit excellent melt flow and low stickiness, giving pinhole-freeskins. These characteristics also ensure smaller peeling forces forremoving the skins from the molds.

INVENTIVE COMPOSITIONS 13-15

The materials listed below in Table 7, with the exception of thestabilizers, calcium stearate and the process oil, were blended togetherin a tumbler. The obtained blend was fed into a twin screw extruderthrough a feed hopper, while the process oil was delivered to theextruder through a vent hole. The materials were kneaded and extruded at200° C. and pelletized. The obtained pellets were then immersed inliquid nitrogen, thrown into a turbo mill, and pulverized therein. Theobtained powder was screened to collect only particles passing through asieve of 1000 μm.

                                      TABLE 7                                     __________________________________________________________________________           parts by weight                                                               Composi-                                                                           Composi-                                                                           Composi-                                                                           Composi-                                                                           Composi-                                                                           Composi-                                      Component                                                                            tion 13                                                                            tion 14                                                                            tion 15                                                                            tion 16                                                                            tion 17                                                                            tion 18                                       __________________________________________________________________________    polypropylene                                                                        56   56   56   56   56   56                                            resin.sup.20                                                                         19   19   19   19   19   19                                            H-SBR.sup.21                                                                  POE.sup.22                                                                           9    9    --   --   9    --                                            EPR.sup.23                                                                           --   --   9    9    --   9                                             process oil.sup.24                                                                   12   12   12   12   12   12                                            organic                                                                              0.1  0.3  0.3  0.4  --   --                                            peroxide.sup.25                                                               pigment                                                                              4    4    4    4    4    4                                             Ca stearate                                                                          0.5  0.5  0.5  0.5  0.5  0.5                                           phenolic                                                                             0.1  0.1  0.1  0.2  0.1  0.1                                           antioxidant                                                                          0.1  0.1  0.1  0.2  0.1  0.1                                           phosphite                                                                     antioxidant                                                                   __________________________________________________________________________     .sup.20 CHISSO POLYPRO K7750 ™ (a product of Chisso Corp.), MFR            (230° C., 2.16 kgf): 45 g/10 min                                       .sup.21 DYNARON 1320P ™ (a product of Japan Synthetic Rubber), styrene     content: 10 wt %, MFR (230° C., 2.16 kgf): 3.5 g/10 min                .sup.22 Styrene/ethylene/propylene/styrene block copolymer (SEPS), SEPTON     2063 ™ (a product of KURARAY), styrene content: 13 wt %, MFR               (230° C., 2.16 kgf): 7 g/10 min                                        .sup.23 Ethylene/propylene rubber (EPR), EP914P ™(a product of Japan       Synthetic Rubber), propylene content: 22 wt %, MFR(230° C., 2.16       kgf): 8.6 g/10 min                                                            .sup.24 DIANA ™ Process Oil (a product of IDEMITSU KOSAN), PW: 380         .sup.25 Perhexa 25B40 ™(a product of Nippon Oil and Fats Co., Ltd.),       peroxide content: 40%, oneminute halflife temperature: 179° C.    

Powder slush molding was conducted using the above compositions. Aleather-grained plate (150 mm×150 mm×3 mm) was heated to 250° C. in anoven. 800 g of a composition was spread thereon and made to adhere tothe plate by allowing a time period of 10 minutes. Any material notadhering was removed. The resulting plate was oven heated at 300° C. for60 seconds, removed from the oven, and cooled with water. Finally, askin with a thickness of 0.8 mm was removed from the plate.

For each example, the melt viscosity of the pellets and the tensileproperties of the skin were evaluated by the following methods. The meltviscosity was evaluated by determining the MFR of the pellets accordingto JIS K7210 at 250° C. under a load of 0.325 kgf. The tensileproperties were evaluated by punching a specimen out of each skin usinga JIS No.3 dumbbell die and determining the tensile strength andelongation of each specimen at a pulling rate of 200 mm/min.

The results of these tests are given in Table 8, below.

                                      TABLE 8                                     __________________________________________________________________________                Composi-                                                                           Composi-                                                                           Composi-                                                                           Composi-                                                                           Composi-                                                                           Composi-                                 Property    tion 13                                                                            tion 14                                                                            tion 15                                                                            tion 16                                                                            tion 17                                                                            tion 18                                  __________________________________________________________________________    MFR(250° C., 0.325 kgf)                                                            10.3 20.4 19.5 16.5 7.8  6.7                                      Tensile Strength (N/cm.sup.2)                                                             950  937  803  962  965  826                                      Elongation (%)                                                                            575  625  572  619  683  589                                      JIS A Hardness                                                                            85   83   85   85   86   86                                       __________________________________________________________________________

INVENTIVE COMPOSITION 16

The materials, except the process oil, were blended together in atumbler. The obtained blend was fed into a twin screw extruder through afeed hopper, while the process oil entered the extruder through a venthole. The materials were kneaded and extruded at 200° C. and pelletized.Then, the obtained pellets were subjected to pulverization and powdermolding viscosity and tensile properties were determined in a mannersimilar to that used for Compositions 13-15.

The results of these tests are given in Table 8.

COMPARATIVE COMPOSITIONS 17 AND 18

The materials were kneaded and pelletized in the same manner as thatused for Compositions 13-16, except that no organic peroxide was used.The obtained pellets were subjected to pulverization and power molding.Melt viscosity and tensile properties were determined.

The results of these tests are given in Table 8, above.

It is apparent from the testing of Compositions 13-18 that the melt flowproperties are superior in cases where an organic peroxide is used, withthe other desirable tensile characteristics remaining unchanged.

The foregoing disclosure of specific embodiments is intended to beillustrative of the broad concepts comprehended by the invention.

We claim:
 1. A thermoplastic elastomer composition for powder slushmolding, said composition comprising:a polypropylene resin, ahydrogenated styrene/butadiene rubber, a process oil, and an elastomerexcellent in oil absorbing power selected from the group consisting ofstyrene/ethylene/propylene/styrene block copolymers,styrene/ethylene/butylene/styrene block copolymers, and crystallineolefin/ethylene/butylene/crystalline olefin block copolymers.
 2. Thethermoplastic elastomer composition according to claim 1 wherein thecomposition has a melt flow rate (MFR) of at least 5 g/10 min asdetermined according to JIS K-7210 at 250° C. under a load of 0.325 kgf.3. The thermoplastic elastomer composition according to claim 1 whereinthe weight ratio of the polypropylene resin to the hydrogenatedstyrene/butadiene rubber is between 80:20 and 20:80.
 4. Thethermoplastic elastomer composition according to claim 1 wherein theelastomer excellent in oil absorbing power is present in an amount of 20to 250 parts by weight per 100 parts by weight of the hydrogenatedstyrene/butadiene rubber.
 5. The thermoplastic elastomer compositionaccording to claim 1 wherein the process oil is present in an amount of5 to 200 parts by weight per 100 parts by weight of the elastomerexcellent in oil absorbing power.
 6. The thermoplastic elastomercomposition according to claim 1 including one or more of a heatstabilizer, light stabilizer, pigment, lubricant, and filler.
 7. Thethermoplastic elastomer composition according to claim 6 wherein theheat stabilizer is a combination of a phenolic antioxidant with aphosphite antioxidant.
 8. The thermoplastic elastomer compositionaccording to claim 6 wherein the light stabilizer is one of a hinderedamine and a bensotriazole.
 9. The thermoplastic elastomer compositionaccording to claim 6 wherein the pigment is one of an organic andinorganic pigment suitable for use with olefins.
 10. The thermoplasticelastomer composition according to claim 6 wherein the lubricant is ametal salt of a fatty acid.
 11. The thermoplastic elastomer compositionaccording to claim 6 wherein the filler is one of calcium carbonate andtalc.
 12. A process for the preparation of a thermoplastic elastomercomposition for powder molding, said process including the stepsof:adding at least a hydrogenated styrene/butadiene rubber, a processoil, and an elastomer excellent in oil absorbing power selected from thegroup consisting of styrene/ethylene/propylene/styrene block copolymers,styrene/ethylene/butylene/styrene block copolymers, and crystallineolefin/ethylene/butylene/crystalline olefin block copolymers to apolypropylene resin to produce a mixture; and simultaneously kneadingand heating the obtained mixture.
 13. A process for the preparation of athermoplastic elastomer composition for powder slush molding, saidprocess including the steps of:preparing a blend comprising apolypropylene resin and a hydrogenated styrene/butadiene rubber at aweight ratio in the range of 80:20 to 20:80; adding an elastomerexcellent in oil absorbing power selected from the group consisting ofstyrene/ethylene/propylene/styrene block copolymers,styrene/ethylene/butylene/styrene block copolymers, and crystallineolefin/ethylene/butylene/crystalline olefin block copolymers to theblend in an amount of 20 to 250 parts by weight per 100 parts by weightof the hydrogenated styrene butadiene rubber; adding a process oil in anamount of 5 to 200 parts by weight per 100 parts by weight of theelastomer excellent in oil absorbing power to produce a mixture,kneading and pelletizing the mixture while heating; and pulverizing theobtained pellets with the obtained pellets one of a) at ambienttemperature and b) in a frozen state.
 14. A process for the preparationof a thermoplastic elastomer composition for powder molding, saidprocess including the steps of:adding at least a hydrogenatedstyrene/butadiene rubber, a process oil, an elastomer excellent in oilabsorbing power selected from the group consisting ofstyrene/ethylene/propylene/styrene block copolymers,styrene/ethylene/butylene/styrene block copolymers, and crystallineolefin/ethylene/butylene/crystalline olefin block copolymers and anorganic peroxide to a polypropylene resin to obtain a mixture; andsimultaneously kneading and heating the obtained mixture.
 15. Theprocess for the preparation of a thermoplastic elastomer compositionaccording to claim 14 wherein the step of adding an organic peroxidecomprises the step of adding an organic peroxide selected from amongdiacyl peroxides, peroxy esters, diallyl peroxide, di-t-butyl peroxide,t-butyl cumyl peroxide, dicumyl peroxide,2,5-dimethyl-2,5-di(t-butylperoxy)hexane-3,1,3-bis(t-butylperoxyisopropyl)benzene,and 1,1-dibutylperoxy-3,3,5-trimethylcyclohexane.
 16. The process forthe preparation of a thermoplastic elastomer composition according toclaim 14 wherein the step of adding an organic peroxide comprises thestep of adding an organic peroxide in an amount of 0.02 to 5% by weight.17. The process for the preparation of a thermoplastic elastomercomposition for powder molding according to claim 14 wherein the addingstep comprises the step of adding the organic peroxide in an amount of0.02 to 5.0% by weight of the thermoplastic elastomer composition. 18.The process for the preparation of a thermoplastic elastomer compositionaccording to claim 17 wherein the step of adding an organic peroxidecomprises the step of adding an organic peroxide selected from amongdiacyl peroxides, peroxy esters, diallyl peroxide, di-t-butyl peroxide,t-butyl cumyl peroxide, dicumyl peroxide,2,5-dimethyl-2,5-di(t-butylperoxy)hexane-3,1,3-bis(t-butylperoxyisopropyl)benzene,and 1,1-dibutylperoxy-3,3,5-trimethylcyclohexane.
 19. The process forthe preparation of a thermoplastic elastomer Composition according toclaim 17 wherein the step of adding an organic peroxide comprises thestep of adding an organic peroxide in an amount of 0.02 to 5% by weight.20. The process for the preparation of a thermoplastic elastomercomposition for powder molding according to claim 14 wherein thekneading step comprises kneading at a temperature of 120 to 250° C. 21.A process for the preparation of a thermoplastic elastomer compositionfor powder slush molding, said process including the steps of:preparinga blend comprising a polypropylene resin and a hydrogenatedstyrene/butadiene rubber at a weight ratio in the range of 80:20 to20:80; adding an elastomer excellent in oil absorbing power selectedfrom the group consisting of styrene/ethylene/propylene/styrene blockcopolymers, styrene/ethylene/butylene/styrene block copolymers, andcrystalline olefin/ethylene/butylene/crystalline olefin block copolymersto the blend in an amount of 20 to 250 parts by weight per 100 parts beyweight of the hydrogenated styrene/butadiene rubber; adding a processoil to the blend in an amount of 5 to 200 parts by weight per 100 partsby weight of the elastomer excellent in oil absorbing power; adding anorganic peroxide to the blend in an amount of 0.02 to 5.0% by weight ofthe thermoplastic elastomer composition; kneading and pelletizing theresulting blend while heating; and pulverizing the obtained pellets withthe obtained pellets one of a) at room temperature and b) in a frozenstate.
 22. The process for the preparation of a thermoplastic elastomercomposition for powder molding according to claim 21 wherein thekneading step comprises kneading at a temperature of 120 to 250° C. 23.The process for the preparation of a thermoplastic elastomer compositionfor powder molding according to claim 16 including the step of addingone or more of a heat stabilizer, light stabilizer, pigment, lubricant,and filler.
 24. The process for the preparation of a thermoplasticelastomer composition for powder molding according to claim 18 includingthe step of adding one or more of a heat stabilizer, light stabilizer,pigments, lubricant, and filler.
 25. The process for the preparation ofa thermoplastic elastomer composition for powder molding according toclaim 18 including the step of adding one or more of a heat stabilizer,light stabilizer, pigment, lubricant, and filler.
 26. The process forthe preparation of a thermoplastic elastomer composition for powdermolding according to claim 21 including the step of adding one or moreof a heat stabilizer, light stabilizer, pigments, lubricant, and filler.